ACPAtmospheric Chemistry and PhysicsACPAtmos. Chem. Phys.1680-7324Copernicus GmbHGöttingen, Germany10.5194/acp-9-8223-2009Satellite measurements of formaldehyde linked to shipping emissionsMarbachT.1BeirleS.1PlattU.2HoorP.1WittrockF.3RichterA.3VrekoussisM.3GrzegorskiM.1BurrowsJ. P.34WagnerT.11Max Planck Institute for Chemistry, Mainz, Germany2Institute of Environmental Physics, Heidelberg, Germany3Institute of Environmental Physics, Bremen, Germany4Center for Ecology and Hydrology, Wallingford, UK0311200992182238234This work is licensed under a Creative Commons Attribution 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by/3.0/This article is available from http://www.atmos-chem-phys.net/9/8223/2009/acp-9-8223-2009.htmlThe full text article is available as a PDF file from http://www.atmos-chem-phys.net/9/8223/2009/acp-9-8223-2009.pdf

International shipping is recognized as a pollution source of growing
importance, in particular in the remote marine boundary layer. Nitrogen
dioxide originating from ship emissions has previously been detected in
satellite measurements. This study presents the first satellite measurements
of formaldehyde (HCHO) linked to shipping emissions as derived from
observations made by the Global Ozone Monitoring Experiment (GOME)
instrument.
<br><br>
We analyzed enhanced HCHO tropospheric columns from shipping emissions over
the Indian Ocean between Sri Lanka and Sumatra. This region offers good
conditions in term of plume detection with the GOME instrument as all ship
tracks follow a single narrow track in the same east-west direction as used
for the GOME pixel scanning. The HCHO signal alone is weak but could be
clearly seen in the high-pass filtered data. The line of enhanced HCHO in
the Indian Ocean as seen in the 7-year composite of cloud free GOME
observations clearly coincides with the distinct ship track corridor from
Sri Lanka to Indonesia. The observed mean HCHO column enhancement over this
shipping route is about 2.0&times;10<sup>15</sup> molec/cm<sup>2</sup>.
<br><br>
Compared to the simultaneously observed NO<sub>2</sub> values over the shipping
route, those of HCHO are substantially higher; also the HCHO peaks are found
at larger distance from the ship routes. These findings indicate that direct
emissions of HCHO or degradation of emitted NMHC cannot explain the observed
enhanced HCHO values. One possible reason might be increased CH<sub>4</sub>
degradation due to enhanced OH concentrations related to the ship emissions,
but this source is probably too weak to fully explain the observed values.
<br><br>
The observed HCHO pattern also agrees qualitatively well with results from
the coupled earth system model ECHAM5/MESSy applied to atmospheric chemistry
(EMAC). However, the modelled HCHO values over the ship corridor are two
times lower than in the GOME high-pass filtered data. This might indicate
uncertainties in the satellite data and used emission inventories and/or
that the in-plume chemistry taking place in the narrow path of the shipping
lanes are not well represented at the rather coarse model resolution.